Method for convertion of heat

ABSTRACT

A method for conversion of heat in hot flue gases, vaporisation heat in the flue gases being released and converted into an energy carrier which converts from the liquid phase to gas phase.

[0001] The present invention relates to a method for conversion of heatin hot flue gases whose energy content has fallen to such a level that afurther reduction of energy could entail that the dew points of the fluegases may be fallen beneath in such a manner that the depositions ofliquids cannot be prevented and in which the recovered energy may beconverted into electric power at the same time that the cooling processby evaporative agglomeration entails that small condensed particles aremade heavier and may thereby more readily be separated off from the fluegas.

[0002] We are daily being reminded about how our environment isconstantly deteriorating. There are many explanations, but it isundisputed that the emissions of flue gases into the atmosphere have anot inconsiderable importance. It is, therefore, of paramount importanceto utilise the fuel, the energy source, as far as is possible andconvert the energy into electricity which is that type of energy whichis the easiest to convert into other energy forms, at the same time asthe purification or scrubbing of the flue gases becomes increasingimportant.

[0003] In hot flue gases, there is always water which derives from thefuel and the combustion air, The lower the moisture content in the fuel,the greater the quantity of water in the flue gases. In the combustionof the fuel, a large quantity of energy is consumed in vaporising theincluded water volume and this quantity of energy is bonded in the fluegas throughout the entire combustion cycle as so-called vaporisationheat. Energy cannot be released until the temperature in the flue gasesis less than the dew point of the flue gases, which entails that freewater is deposited at the same time as energy is released.

[0004] As a rule, the flue gases include many other substances such as,for example sulphur and which, in the combustion process, is convertedinto for example SO₂ and SO₃. At different temperatures, the condensedwater reacts with, for example SO₃ which then becomes H₂SO₄, sulphuricacid. This sulphuric acid is corrosive and causes corrosion on thematerials which are normally employed in flue gas ducts, chimneys etc.Further, a far-reaching temperate reduction entails that the dust whichexists in the flue gases becomes tacky and, as a rule, obtainsconsiderable adhesive power with the result that flue gas ducts, boilertubes, chimneys etc. may easily become blocked, with operationdisruption as a result. In order to avoid these operational disruptionsand/or operational stoppages for repair and cleaning, the temperature ofthe flue gases is seldom reduced in the boiler which is provided forenergy to be able to be converted to steam or hot water to temperatureswhich are less than 200° C. Variations naturally occur depending on fuelcombustion equipment boiler, flue gas scrubbing equipment, chimney andalso the prevailing environmental requirements.

[0005] The present invention makes possible a profitable investmentsince recovered energy is converted Into electricity and at the sametime a superior cleaning or scrubbing effect will be obtained of theflue gases with a method which in principle takes place in nature but inthe manner described here under completely controlled vaporisation heatin the flue gas is released and converted into an energy carrierpossessing a specific property which, from the liquid phase, converts tothe gas phase and which is superheated at a constant pressure by theflue gas before it has assumed a condensing state with the aid of waterwhich bas been finely divided with the aid of ultrasound and which israpidly vaporised in the flue gas stream because the water had also beenpreheated in a condenser where the energy carrier had condensed with theaid of the water once the energy carrier had given off much of itsenergy content by an isentropic expansion in an expander connected to agenerator. The energy carrier is characterised in that it has lowvaporisation heat and that it is capable of carrying high enthalpy atlow temperature.

[0006] In the temperature reduction of the flue gases, a considerablequantity of water is released which contains numerous pollutants, fromlarge dust particles to heavy metals which have condensed to particles,and acids which are formed such as, for example hydrochloric acid andsulphuric acid, The condensate must be purified before it is released toa recipient. If the flue gases had been released into the atmospherewithout the above-described process, these pollutants would have beenspread into nature. Tho present invention further entails that,depending on fuel quality, moisture content etc., up to approx. 35%additional energy can be recovered without extra fuel needing to besupplied. The economisation of fuel for future generations regardless ofwhether we save e.g. oil, natural gas, coal or biomass fuel willprobably be of major importance.

[0007] Instead of, as in conventional plants, allowing the flue gas tobe released into the atmosphere once the energy content ha been utilisedas far as possible, the present invention entails a considerably greaterenergy yield at the same time as much of the pollutants included in theflue gases are separated off and the degree of utilisation, orefficiency, of the fuel supplied is considerably improved.

[0008] A plant according to the present invention is exemplified on theaccompanying drawing, and the diagrams exemplify the principle of themethod according to the present invention.

1. A method for conversion of heat in hot flue gases, characterised inthat vaporisation heat in the flue gas is released and converted into anenergy carrier which converts from the liquid phase to gas phase.
 2. Themethod as claimed in claim 1, characterised in that the energy carrieris superheated at a constant pressure of the flue gas.
 3. The method asclaimed in claim 1 or 2, characterised in that the steps take placeprior to the transition to condensed state with the aid of water.
 4. Themethod as claimed in claim 3, characterised in that the water is finelydivided by means of ultrasound.
 5. The method as claimed in claims 3 and4, characterised in that the water is rapidly vaporised in the flue gascurrent by the water having been preheated in a condenser.
 6. The methodas claimed in claim 5, characterised in that the energy carrier iscondensed with the aid of the water after the energy carrier has givenoff energy by an isentropic expansion in an expander which is connectedto a generator.
 7. The method as claimed in claims 1 and 6,characterised in that the energy carrier is selected from among thoseenergy carriers which have low vaporisation heat and which have thecapacity for high enthalpy at low temperature.